1. Field of the Invention
This invention relates to a device for positioning and maintaining horizontal tension on paper computer forms of varying width.
2. Description of Prior Art
In the field of computer peripherals, an important feature of high speed printers is the ability to accept paper computer forms of different widths and weights.
Conventional high speed printers utilize paper forms which have perforations along their edges. When the paper enters the printer, it comes in contact with two paper tractors which have small protrusions which engage the perforations. As the tractors turn, the paper is transported into the printer and past a printing mechanism.
In such printers, the positioning of the paper relative to the printing heads is critical if the printed output is to be properly centered on the paper. Therefore, it is important to maintain the paper tractors in the proper positions relative to the locations of the printing mechanism. An additional requirement is that the horizontal tension of the paper across the printing mechanism be maintained, thereby insuring a clean even print on the paper. These requirements are met by adjusting the positions of the tractors individually to achieve the proper separation for a particular width paper, and in tandem from side to side to accurately position the entire sheet of paper.
Traditionally, paper tractor positioning is achieved by positioning the tractors on a shaft and linking them mechanically so that they move in unison. This system does not accommodate paper forms of varying widths. Other systems which have been used have proven to be overly complex.
Some printers utilize two vertically aligned pairs of tractors to move the paper. These printers generally have no provision for realigning the upper and lower tractors if they fall out of vertical alignment relative to one another. In addition, most prior art methods require the major portion of horizontal tractor adjustment to be made by manually sliding or moving the tractors to a general location, and then fine adjusting the tractors to the final position by means of an additional knob or knobs. In addition to the above disadvantages, these systems employ a number of shafts, machined brackets and supports, so that they take up an unnessary amount of space and cannot be easily adapted to a modular design. Because of this the cost of manufacture and installation of most prior art systems has been fairly high.
It is one objective of the present invention to provide a paper form positioning and retaining apparatus which does not depend upon a complex series of shafts or plates for its adjustment. It is another objective of the present invention to provide an apparatus which may be quickly and easily adapted to accept paper forms of different widths, and to adjust the horizontal tension thereon, using a single control mechanism.
It is yet another objective of the present invention to provide an adjustment means for two pairs of vertically spaced tractors or tractor supports, wherein the vertical alignment of the tractors may be verified by recalibration to a base position without the need to disassemble the printer.
It is another objective of the present invention to provide a device which is modular in construction, easy to assemble, and low in cost.